Vulnerability in PyJWT (CVE-2026-102272)
Summary
Vulnerability in PyJWT (CVE-2026-102272). Confidential information can be exposed externally. Exploitable via pyjwt. Mitigation: upgrade to 2.14.0 or later.
Original description
The description as published by the source.
Affected Package
- Package: PyJWT (
pyjwton PyPI) - Repository: https://www.google.com/url?q=https://github.com/jpadilla/pyjwt&source=gmail&ust=1781794518474000&sa=E
- Affected version: 2.13.0
- Vulnerability class: Algorithm confusion / patch bypass
Root Cause
PyJWT 2.13.0 introduced a guard in HMACAlgorithm.prepare_key() (file jwt/algorithms.py, approximately line 344) to prevent RSA public key material from being used as an HMAC secret — the root cause of CVE-2026-48526.
The guard uses bytes.lstrip() before calling startswith(b"{"):
stripped = key_bytes.lstrip() # strips ASCII whitespace only
if stripped.startswith(b"{"): # JWK detection
...
raise InvalidKeyError("The specified key is an asymmetric key...")
bytes.lstrip() with no argument removes only bytes in the ASCII whitespace set (\x20 \t \n \r \x0b \x0c). A UTF-8 BOM prefix (\xef\xbb\xbf) is not stripped, so stripped.startswith(b"{") returns False for any BOM-prefixed JWK JSON. The JWK detection block is never entered, and the RSA public key bytes are silently accepted as the HMAC-SHA256 secret.
PoC Sketch (pseudocode — not a weaponized payload)
# 1. Attacker obtains RSA public key JWK (e.g., from /jwks.json endpoint)
# and prepends a UTF-8 BOM byte sequence before the JSON opening brace.
# 2. Attacker signs a JWT using HS256, with the BOM-prefixed JWK as the secret.
# 3. Attacker submits the forged token to a verifier that:
# -…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-102272 has been found in PyJWT.
Attackers can target a specific entry point like pyjwt over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade PyJWT to 2.14.0 or later.
If unsure, ask your IT team or search "PyJWT CVE-2026-102272" on the vendor's site.
CVE-2026-102272 (PyJWT) — CWE-347 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: pyjwt / False / PyJWK / kty
Patched: 2.14.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-347) exists in PyJWT. Attackers reach the vulnerable code path via pyjwt without authentication.
Check the vendor advisory for the affected versions of PyJWT. Attack surface: pyjwt / False / PyJWK / kty.
Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.
Update to 2.14.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'PyJWT' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'PyJWT' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
PyJWTを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade PyJWT to 2.14.0ステージング環境で 2.14.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com